Submarine cable signaling system



Aug. 8, 1933.

E. T. BURTON SUBMARINE CABLE SIGNALING SYSTEM Filed July 25, 1931 All{AMPLIFIER comvsc TOR i C ORPE C TOP DIRECT VOL TAGE #(ljNPUT TO FIRSTSTAGE OF AMPLIFIER 24 /COPPEC TING VOL TAGE, /N OPPOSITE PHASE msous/vcINVENTOR E. 7TBUR TON ATTORNEY Patented Aug. 8, i933 PATENT OFFICESUBMARINE CABLE SIGNALING SYSTEM Everett T. Burton, Millburn, N. .l.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a Corporation of New York Application July 25, 1931. Serial No. 553,100

5 Claims.

This invention relates to signal transmission systems and moreparticularly to receiving systems for use in connection with submarinecables or other high electrostatic capacity conductors.

An object of the invention is to correct for the effects known as zerowander" in a highly eificacious manner.

It is well known in the art that in signaling over high capacity cables,such as submarine cables, by means of positive and negative impuses,earth currents or a temporary preponderance of impulses of one polaritywill cause an accumulative charging effect in the cable which manifestsitself as an apparent shifting of the zero line in the direction of theimpulses which, for the time being, predominate. The distorted signalwave arriving at the receiving end of the cable may, in other words, besaid to consist of two components; one, the high frequency signalingcurrent reversals sent out by the transmitting station, and the other, alow frequencyvariation representing the fluctuating charge on the cablefollowing the momentary preponderance of impulses-of one or the otherpolarity.

When the receiving apparatus is a siphon recorder, the shifting of thezero, or, as it is commonly called zero wander, is of relatively minorimportance, but when relays are to be operated, it becomes essential tolimit theamplitude of zero wander effects to a rather small proportionof the total signal impulse amplitude. If the shifting of the zerobecomes, for example, more than twenty per cent of the normal signalamplitude of the current in the relay winding of the receiving circuit,the amplitude of the signal impulse may not be suflicient to move thearmature of the relay into engagement with one of its contacts and therelay will fail to operate thus rendering the signal unintelligible. Inthe case .of printing telegraph systems, where the apparatus at theopposite end of the cable must be held in synchronism, the uncertaintyof the operation of relays caused by zero wander in turn causes seriousvariations in synchronism and may make operation impossible.

According to the present invention, the zero wander is corrected byconnecting across the primary winding of an input transformer in areceiving circuit an auxiliary circuit wherein a portion of the earthcurrents due to earth potentials on the cable and of the extremely lowfrequency components on the received signals,

are-amplified and then impressed back on the receiving circuit inopposite phase to the portion of earth currents and the low frequencycomponent remaining in the latter circuit at a point in front of thereceiving amplifier, whereby any shift in the zero line of the incomingsignal wave before amplification is prevented.

A feature of the invention is the use of an auxiliary circuit whereinthe currents themselves which produce zero wander effects are utilizedfor restoring the zero line of the received signals to its trueposition.

Another feature resides in the continuous operation of the correctingsystem.

Still another feature is that the zero wander correction is effective inthe input of the first stage of amplification of the received signals.

Other objects and features will be found in the following detaileddescription and appended claims considered in conjunction with theaccompanying drawing of which Fig. 1 shows a preferred embodiment of theinvention;

Figs. 2 and 3 show modifications of Fig. .1;

Fig. 4 shows a graphic representation of the operation of the system.

Like parts are designated by like reference characters.

Referring to Fig. 1, incoming signals are received over conductor 11-ofcable 12 and shaping network 13 and impressed on the primary winding 14of input transformer 15, whereby the input energy comprising both thehigh frequency signal components and the low frequency variation, due tothe fluctuating charge on the cable, is impressed on the grid of vacuumtube 16 which represents the first stage of the amplifier 24. The lowfrequency variation which fluctuates from one polarity to the othercauses the zero of the signal wave in the output circuit of tube 16 towander from one side to the other of its true position depending uponthe predominating polarity in the incoming signal wave. This zero wanderis greatly increased in subsequent stages (not shown) of the amplifier,so that in the output circuit of the last stage, the output signal wavewill reach such value that a polar relay (not shown) arranged to receivethe ultimate output will be responsive to signal impulses of onepolarity only. This condition is overcome by connecting across theprimary winding 14 an auxiliary circuit 17 comprising a low pass filter18, a vacuum tube amplifier 19, condenser 20 of relatively largecapacity, an adjustable network 21 and a primary winding 22 ofcomparatively high inductance, of transformer 23. The auxiliary circuitallows the low frequency components only of the incoming signal wave topass and be impressed on the grid circuit of tube 16. The output of theauxiliary circuit is impressed on the input circuit of tube 16 but inopposite phase to the energy transmitted from transformer 15 andtherefore neutralizes the low frequency variations in the input voltageof tube 16 so that a signal wave having a true zero position passesthrough tube 16, and the subsequent stages to one or more polar relays(not shown). The correct operation of the polar relays provides properlytimed impulses which may be utilized for securing true synchronizationfor the system.

In Fig. 2 is shown a modification of Fig. 1 wherein the auxiliarycircuit 17 is inductively coupled to the primary winding 14 as shown toreceive the input voltage. The output of the auxiliary circuit is hereimpressed across the variable resistance 25 in opposite phase to thegrid voltage of tube 16 whereby the low frequency variations in the gridvoltage are neutralized and the signal wave having a true zero position,passes through the first stage of the amplifier representeddiagrammatically by block 24.

The modification shown in Fig. 3 is the same as Fig. 1 except for themanner of impressing the output of the auxiliary circuit on the inputvoltage on the first stage of amplifier 24. In Fig. 3 a variableresistance 25 is used in place of transformer 23.

The amplitude frequency characteristic of the arrangements shown inFigs. 1, 2 and 3 is depicted in Fig. 4. The voltage of an incomingsignal wave is indicated by curve a beginning at point X. The output ofthe auxiliary circuit 1'7 is indicated by curve b also beginning atpoint X and shown as being in opposite phase to curve a. The effect ofcurve b on curve a is shown in curve 0 which is the difference betweencurves a and b, and represents the corrected input voltage impressed onthe first stage of amplifier 24 wherein the ground currents aresubstantially eliminated.

What is claimed is:

1. A receiving system comprising input terminals for connecting saidsystem to a transmission line, a main path and an auxiliary pathconnected in parallel relation to receive currents impressed on saidinput terminals and having their output terminals connected to eachother in opposing relation, means in one of said paths to suppresstransmission therethrough of signal currents of essential deep sea cabletelegraph frequencies but which transmits currents of a range of lowerfrequencies, and means in said last-mentioned path to increase theamplitude of said transmitted lower frequency currents to a magnitudeapproximately sufiicient to annul the similar frequency currentstransmitted by said other path.

2. A cable receiving circuit comprising input terminals, an amplifier,means connecting said input terminals to raid amplifier to transmitthereto signal currents and zero wander impulses impressed on said inputterminals, and additional means connecting said input terminals to saidamplifier to transmit thereto zero wander impulses to the exclusion ofsignal currents and of an intensity equal to and phase opposite to thosetransmitted by said first-mentioned means whereby the resultant currentstransmitted to said amplifier comprise signal currents substantiallyfree from zero wander effects.

3. A signal wave transmission line over which signal currents involvingcomponents of a range of essential frequencies are transmitted, a maintransmission circuit electrically connected to said line to receivetherefrom signal currents and casual disturbance currents oflowerfrequencies, and an auxiliary circuit having its input terminalsconnected to said line and its output terminals connected to saidtransmission circuit, said auxiliary circuit having means therein totransmit freely currents of a range of frequencies below said essentialfrequency range but which suppresses currents impressed thereon offrequencies'higher than said transmitted range, said auxiliary circuithaving its output terminals connected to said transmission circuit insuch manner as to oppose therein currents of the frequencies which saidauxiliary circuit transmits.

4. In combination, a deep sea cable receiving circuit comprising intandem means for connecting said circuit to a deep sea cable, a shapingnetwork, a transformer and a main transmission circuit, a circuitauxiliary to the tandem apparatus having its input terminals connectedto a winding of said transformer and its output posing thols" directlytransmitted to said transmission circuit from said transformer, andmeans in said auxiliary circuit to limit the range of currents which ittransmits to frequencies of the order of those encountered in zerowander effects.

5. A deep sea cable terminal receiving circuit comprising a maintransmission circuit adapted to be connected to a cable and having atransmission frequency range which includes the essential range ofsignal frequencies to be transmitted over said cable, means forconnecting said transmission circuit to said cable, and an auxiliarycircuit having its input terminals connected to said cable and itsoutput terminals connected to said transmission circuit in such manneras to supply currents thereto to oppose those of the same frequencytransmitted directly from said cable to said transmission circuit, saidauxiliary circuit including low pass filter having a transmission rangebelow the essential range of signal frequencies but including lowfrequencies of the casual currents producing zero Wander efiect wherebysaid zero wander effect is neutralized without neutralization of saidessential signal frequencies.

